Method of impregnating paper to reduce curling tendency and resultant article



United States Patent METHDD 0F IMPREGbIATIN G PAPER TO REDUCE CURLINGTENDENCY AND RESULTANT ARTI- CLE Oscar Bertil Otto Nycander, Sundasen,and Svenning Natanael Carlsson, Ludvika, Sweden, assignors to M0 OchDomsjo Aktieholag, Ornskoldsvik, Sweden, a corporation of Sweden NoDrawing. Filed Feb. 7, 1964, Ser. No. 343,229

11 Claims. (Cl. 96-85) The present invention relates to an impregnatingcomposition for reducing the tendency to curling of paper and paper-likematerials, in particular photographic paper, a paper or paper-likematerial impregnated with the composition and a method of impregnatingpaper and paperlike materials with the composition.

A problem of many cellulose sheet materials, in particular paper andpaper-like material, is that under storage they show a strong tendencyof curling on account of variations in air moisture. In particularpaper-s coated with light-sensitive or thermosensitive materials, suchas photographic papers, exhibit this tendency. This curling involvesgreat difiiculties in storage and handling of the materials, e.g. in thecase of drawings, which are stored at a work place or in copying suchmaterials.

Many attempts have been made to solve this problem, e.g. by impregnatingthe paper with low molecular weight alcohols or mixtures thereof. Suchimpregnations have initially given a relatively good resistance tocurling, but the effect has disappeared already after a short time forvarious reasons, among them the volatility of the impregnating agent.Attempts have also been made to use higher polyalcohols, which onaccount of their greater molecular weight are not so volatile, and suchsubstances have been shown to give a very good and lasting eifect, butthey show a tendency of being absorbed very slowly or not at all in thematerials to be impregnated.

An object of the present invention is to provide an impregnatingcomposition for reducing the curling tendency of paper or paper-likematerials, which composition is free from the aforementioneddisadvantages. Another object is to provide an impregnating compositionfor. the purpose referred to, which is readily absorbed by paper andpaper-like materials and provides a lasting resistance to curling ofpaper and paper-like materials treated therewith. A turther object is toprovide an improved method of treating paper and paper-like materials,in particular such materials coated with photosensitive orthermosensitive substances, by which method such materials can be maderesistant to cur-ling in a more eflicient way. A still further object isto provide paper and paper-like materials which have a lastingresistance to curling.

The impregnating composition of this invention comprises one or moreWater-soluble polyalkylene glycols having a molecular weight of 100 to6000 and a substance enhancing the absorption of the polyalkylene glycolin Patented Jan. 31, 1967 ice alone, however, a lower rate of absorptionis obtained than with the additives referred to.

The poly-alkylene glycol or glycols employed should have a molecularweight such that they do not vaporize too readily from the paper, but onthe other hand they should not have too high molecular weight, sincethen the impregnation of the paper is rendered difficult by the highviscosity and decreasing ability of penetration of the polyglycol. It ispreferable to use a polyalkylene glycol or mixture of polyalkyleneglycols having a molecular weight of between 500 and 1000. The mostpreferred polyalkylene glycol is polyethylene glycol, althoughpolypropylene glycol, polybutylene glycol etc. in suitabe molecularweights are also useful. It is also possible, in accordance with thisinvention, to use mixtures of difierent polyalkylene glycols wherein thealkylene groups are ditterent e.g. polyethylene glycol and polypropyleneglycol, or mixtures of the same polyalkylene glycol in differentmolecular weights.

Suitable water-soluble polyhydric aliphatic alcohols having 2 to 15carbon atoms are dihydric, trihydric and higher aliphatic saturated orunsaturated alcohols, such as ethylene glycol, glycerol, propyleneglycol, polyalkylene glycols having a molecular weight of not above 250,sorbitol, mannitol, pentaerythritol, 1,4-butanediol, 2,3 butanediol,1,3-propanediol, 1,2-pentanediol, 1,4-pe-ntanediol, 1,5-pentanediol,2,3-pentanediol etc.

A suitable formulation of the composition according to the invention isfrom 0.2 to 5 parts by weight of the water-soluble polyhydric alcoholper part by weight of the polyalkylene glycol component having amolecular weight of between and 6000. For use such a composition issuitably diluted from 0:2 to- 50 parts by weight of water per part byweight of the polyalkylene (glycol component, e.g. so that thecomposition contains from about 5 to about 30% by weight of thepolyalkylene glycol component, based on the whole composition.

impregnation of paper with this composition can be carried out bywell-known methods such as dipping or spraying methods. In the case of apaper or paper-like material coated with a photosensitive orthermosensitive layer, the composition can be introduced either beforeor after application of the photosensitive or thermosensitive coating.

The invention is illustrated by but not limited to the followingexamples, which shOW various compositions within the scope of theinvention as well as the results obtained therewith as regards theabsorption of polyalkylene glycol by photographic paper. Percentages areby weight.

Example 1 Impregnating baths were prepared which contained each 108 g.of polyethylene glycol (molecular weight 600) and 730 g. of watertogether with (a) 110 g. of ethylene glycol and 84 g. of glycerol, (-b)194 g. of ethylene glycol, (c) 194 g. of glycerol, and (d) 194 g. ofpropylene glycol. For comparison, a bath (e) was also prepared whichcontained 108 g. of the same polyethylene glycol and 924 g. of water.

Sheets of Kodak Projection Document Paper, Medium Weight, Statefile 84,in A5 size were developed 1 minute, dipped in water, fixed for 10minutes and thereupon immersed without prior rinsing in the polyglycolimpregnating bath for 10 minutes. When the sheets were taken up from thepolyglycol bath they were allowed to drain for 30 seconds, whereuponthey were dried in a photodrier.

Thereupon, the amount of polyglycol taken up by each sheet wasdetermined in the following manner: The sheet was extracted in aS-oxhlet apparatus with chloroform for 2 hours, the apparatus beingemptied 10 to 15 times. The major portion of the chloroform wasevaporated from the extract, whereupon water was added and the remainingchloroform evaporated. The aqueous solution was filtered and diluted to100 ml. In this solution the amount of polyglycol was determined byprecipitation with potassium ferrocyanide, filtration and back-titrationwith cerium ammonium sulfate.

The following results were obtained Polyethylene glycol taken up bypaper in mg. Average Bath: of 4 sheets (a) 159 (b) 163 (c) 183 (d) 178(e) 103 The results show that the aliphatic alcohols considerablyincrease the absorption of the polyalkylcne glycol by the paper.

Example 2 The following impregnating baths were prepared.

Percent Polyethylene glycol (molecular weight 1000) 1O Glycerol 20 Water70 Polyethylene glycol (molecular weight 1000) 10 Water 90 Polyethyleneglycol (molecular weight 1000) 30 Polyethylene glycol (molecular weight200) 20 Water 50 Polyethylene glycol (molecular weight 1000) 30 Water 70In each test, there were used two photopapers Kodak Projection DocumentPaper, Medium Weight, Statefile 84 of A4 size which were divided in twoto obtain four A size sheets for each test. The four sheets weredeveloped 1 minute, dipped in water, and fixed for minutes. Withoutprior rinsing, each sheet was then immersed in 250 ml. impregnating bathfor 10 minutes. After the sheets were taken up from the baths, they wererun through a wringing machine and then dried for 20 minutes on aphotodrier at about 100 C. The amount of polyethylene glycol ofmolecular weight 1000 taken up by each sheet was determined by thetechnique described in Example 1. The following results were obtained.

Amount of polyglycol (mol. w. 1000) absorbed, in mg. Bath: Average of 4sheets (a) 43 (b) 26 (c) 208 (d) 184 The table shows that both thepolyethylene glycol of molecular weight 200 and the glycerolconsiderably increased the absorption of polyethylene glycol.

Example 3 By the procedure described in Example 1, the absorption ofpolyethylene glycol (molecular weight 600) from baths containing varyingamounts of ethylene glycol was determined. The composition of theimpregnating baths and the results obtained are shown in the followingtable.

Bath Composition, percent Absorbed amount of polyethylene glycol in mg.Average of 4 Polyethylene Ethylene Water sheets glycol glycol It isclearly seen from the table that in every case, the addition of ethyleneglycol resulted in a significant increase of the amount of polyethyleneglycol absorbed as compared to impregnating baths without this addition.

Example 4 To determine the time to be gained by adding a polyhydriclower aliphatic alcohol in accordance with this invention, the followingtests were made.

Photopaper' sheets of the same type as in Example 1 were divided in two,developed for 1 minute, dipped in water and fixed for 10 minutes. Onehalf was immersed in a bath (a) comprising 10% of polyethylene glycol(molecular weight 600) and 90% of water, the other half in a bath (b)comprising 10% of polyethylene glycol (molecular weight 600), 20% ofethylene glycol and 70% of water. The test was repeated with varyingtimes of immersion. After the sheets had been removed from the baths,they were run through a wringer and then dried for 20 minutes in aphotodrier at about C. The amount of polyethylene glycol absorbed byeach sheet was determined by the technique described in Example 1. Theresults are set forth in the following table, wherein each value is anaverage of two tests.

Bath Immersion time, Absorbed amount of minutes polyglycol, mg.

a, 5 45 b 5 56 a 10 58 10 62 15 54 15 69 The table shows that thepolyglycol is taken up more rapidly from a bath containing ethyleneglycol. In the latter case, practically the same amount of polyglycol istaken up in 5 minutes as is taken up in 10 minutes when no ethyleneglycol is used.

We claim:

1. A method of reducing the curling tendency of paper and paper-likematerials and photographic paper, which comprises applying to the paperan impregnating composition consisting essentially of a water-solublepolyalkylene glycol having a molecular weight within the range from 100to 6000, and a water-soluble polyhydric aliphatic alcohol facilitatingthe absorption of the polyalkylene glycol in the paper, and having fromabout two to about fifteen carbon atoms, the polyhydric alcohol being inan amount within the range from 0.2 to 5 parts by weight per part byweight of the polyalkylene glycol.

2. A method in accordance with claim 1, in which the polyalkylene glycolis a polyethylene glycol having a molecular weight of from 100 to 1000.

3. A method in accordance with claim 1, in which the Water-solublepolyhydric aliphatic alcohol is selected from the group consisting ofglycerol, ethylene glycol,

propylene glycol and polyethylene glycols having a molecular weight ofnot over about 250.

4. A method in accordance with claim 1, in which the compositioncomprises a mixture of polyalkylene glycols.

5. A method in accordance with claim 1, in which the compositioncomprises from 0.2 to 50 parts by weight of water per part by weight ofthe polyalkylene glycol.

6. A method in accordance with claim 1, which comprises applying thecomposition to the paper by dipping.

7. A process in accordance with claim 1, which comprises applying thecomposition to the paper by spraying.

8. Paper having a reduced tendency to curl and impregnated with acomposition consisting essentially of a water-soluble polyalkyleneglycol having a molecular weight Within the range from 100 to 6000, anda waters-oluble polyhydric aliphatic alcohol facilitating the absorptionof the polyalkylene glycol in the paper, and having from about two toabout fifteen carbon atoms, the polyhydric alcohol being in an amountwithin the range from 0.2 to 5 parts by weight per part by weight of thepolyalkylene glycol.

9. Photographic paper having a reduced tendency to curl and impregnatedwith a composition consisting essentially of a water-solublepolyalkylene glycol having a molecular weight within the range from 100to 6000, and a water-soluble polyhydric aliphatic alcohol facilitatingthe absorption of the polyalkylene glycol in the paper, and having fromabout two to about fifteen carbon atoms, the polyhydric alcohol being inan amount within the range from 0.2 to 5 parts by weight per part byweight of the polyalkylene glycol.

10. Paper coated with a photosensitive material and impregnated with acomposition consisting essentially of a water-soluble polyalkyleneglycol having a molecular weight within the range from to 6000, and awatersoluble polyhydric aliphatic alcohol facilitating the absorption ofthe polyalkylene glycol in the paper, and having from about two to abouttwo to about fifteen carbon atoms, the polyhydric alcohol being in anamount within the range from 0.2 to 5 parts by weight per part by weightof the polyalkylene glycol.

11. Paper coated with a thermosensitive material and impregnated with acomposition consisting essentially of a water-soluble polyalkyleneglycol having a molecular weight within the range from 100 to 6000, anda watersoluble polyhydric aliphatic alcohol facilitating the absorptionof the polyalkylene glycol in the paper, and having from about two toabout fifteen carbon atoms, the polyhydric alcohol being in an amountwithin the range from 0.2 to 5 parts by weight per part by weight of thepolyalkylene glycol.

References Cited by the Examiner UNITED STATES PATENTS Re. 24,011 5/1955Ericks 117 156 X 748,179 12/1903 Fowler et al 117-156 X 2,577,734 12/1951 Brinker 26027 2,823,138 2/1958 Hoffman 106-311 2,865,792 12/1958Gray 117-34 2,875,055 2/1959 Griggs et a1. 96--85 MURRAY KATZ, PrimaryExaminer.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,301,680 January 31, 1967 Oscar Bertil Otto Nycander et al.

It is hereby certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

Column 6, line 7, for "about two to about two to about fifteen" readabout two to about fifteen Signed and sealed this 17th day of October1967.

(SEAL) Attest:

Edward M. Fletcher, Jr. EDWARD J. BRENNER Attesting Officer Commissionerof Patents

1. A METHOD OF REDUCING THE CURLING TENDENCY OF PAPER AND PAPER-LIKEMATERIALS AND PHOTOGRAPHIC PAPER, WHICH COMPRISES APPLYING TO THE PAPERAN IMPREGNATING COMPOSITION CONSISTING ESSENTIALLY OF A WATER-SOLUBLEPOLYALKYLENE GLYCOL HAVING A MOLECULAR WEIGHT WITHIN THE RANGE FROM 100TO 6000, AND WATER-SOLUBLE POLYHYDRIC ALIPHATIC ALCOHOL FACILITATING THEABSORPTION OF THE POLYALKYLENE GLYCOL IN THE PAPER, AND HAIVNAG FROMABOUT TWO TO ABOUT FIFTEEN CARBON ATOMS, THE POLYHYDRIC ALCOHOL BEING INAN AMOUNT WITHIN THE RANGE FROM 0.2 TO 5 PARTS BY WEIGHT PER PART BYWEIGHT OF THE POLYALKYLENE GLYCOL.